Researchers have captured the first three-dimensional images of changes in shape, composition, and position of individual catalyst particles during electrochemical cycling.

Movement and coalescence of catalyst particles in response to aging in fuel cells. Left panel: 3-D image of nanoparticles before (yellow) and after (red) electrochemical aging on the carbon support (blue), with arrow showing the motion of a catalyst nanoparticle. Right panel: catching a coalescence event in the act.

The Science

Researchers have developed non-destructive methods to track, in 3-D, the paths and morphologies of platinum cobalt (Pt-Co) fuel cell catalysts during electrochemical cycling. Analysis of images of hundreds of particles led to the discovery that the catalyst nanoparticles coalesced during fuel cell operation; the larger particles reduce the electrocatalytic activity.

The Impact

Detailed understanding and insights into catalyst degradation mechanisms and associated performance loss may enable the design of lower cost, higher performance and more durable fuel cells.

Summary

Proton exchange membrane fuel cells (PEMFCs) represent a higher efficiency and environmentally-friendly alternative to the internal combustion engine used in automobiles, but commercialization is limited due to the degradation of the cathode catalyst that is critical to fuel cell operation. Previous work to understand catalyst degradation mechanisms after electrochemical aging involved destructive techniques that precluded making repeated observations of the same particle over time. The Energy Materials Center at Cornell (emc2), an Energy Frontier Research Center (EFRC), designed and performed experiments to use non-destructive 3-D tomographic methods to track the trajectories and morphological changes of over 300 Pt-Co nanocatalyst particles on a fuel cell carbon support as they aged during electrochemical cycling. The EFRC researchers discovered that coarsening was dominated by the movement and coalescence of the nanocatalyst particles into multicore particles rather than the result of carbon support degradation or a ripening process (larger nanoparticles growing at the expense of smaller ones). These results suggest that minimizing nanocatalyst particle movement, possibly by using functional groups on the carbon support to slow down particle movement, should extend the performance of fuel cells.

Contact

Funding

DOE Office of Science Basic Energy Sciences program, Energy Frontier Research Centers (EFRC) Program; preliminary work (Y.Y.) was supported by DOE Office of Science Basic Energy Sciences program Materials Sciences and Engineering division. This work used the electron microscopy facility of the Cornell Center for Materials Research, supported by the National Science Foundation. Tomography support (R.H.) from National Science Foundation. J.A.M. (EELS analysis) supported by a National Defense Science and Engineering fellowship.